1. Field of the Invention
The present invention relates to a blow-by gas recirculation apparatus to allow blow-by gas generated in an engine to flow in an intake passage to return to the engine, and more particularly to a failure detection device configured to detect a failure of the recirculation apparatus.
2. Related Art
Conventionally, as a technique of the above type, there is known a blow-by gas recirculation apparatus disclosed for example in JP-A-10-184336 (1998). This recirculation apparatus is provided with a blow-by gas recirculation passage provided between a crank case (or a cylinder head cover) of an engine and an intake passage downstream of a throttle valve and a PCV valve provided in the recirculation passage to operate in response to negative pressure. The PCV valve is arranged to adjust its opening degree by a differential pressure between the pressure exerted on an inlet side of the PCV valve and the pressure exerted on an outlet side to thereby regulate a gas flow rate in the blow-by gas recirculation passage. Herein, when a negative pressure is generated in the intake passage during operation of the engine, blow-by gas containing unburned fuel components is caused to flow in the intake passage through the PCV valve and the blow-by gas recirculation passage and thus return to a combustion chamber of the engine. By this recirculation, the blow-by gas can be supplied and treated together with fuel without leaking to atmosphere.
Further, JP-A-10-184336 discloses a failure detection device for the blow-by gas recirculation apparatus. This failure detection device is provided with a gas pressure sensor to detect gas pressure in a blow-by gas recirculation passage and an electronic control device (ECU) to make a determination based on the pressure detected by the gas pressure sensor as to whether or not the blow-by gas recirculation passage is failed.